Field of the Invention
The present invention relates to the use of a condensing heat exchanger system (“CHX”) and increasing the condensation of water and acid from flue gas. In one embodiment, the present invention relates to the use of condensing heat exchanger system installed in fossil power plant applications. More particularly, the present invention relates to a method of modelling a CHX system that decreases water consumption, increases energy efficiency, and lowers capital costs associated with fossil power plants. The present invention is also related to reducing the release of acids into the environment through flue gas. The present invention is also related to a system designed according to the model.
The present invention is related to articles entitled “Theoretical prediction of sulfuric acid condensation rates in boiler flue gas” published in the International Journal of Heat and Mass Transfer 55 (2012) 8010-8019; “Modeling of Heat Recovery from a Steam-Gas Mixture in a High-Temperature Sorption Process” published in the AIChE Journal, Vol. 58, No. 1, pages 312-321; “Analytical modeling of water condensation in condensing heat exchanger” published in the International Journal of Heat and Mass Transfer 53 (2010), 2361-2368.
Background of the Invention
Water supply issues are increasing in importance for new and existing power plants because the freshwater supply is limited. For companies considering the development of new thermoelectric power plants, water is a first-order concern. The impacts of water supply depend on the economics of water availability in the region in which the power plant is to be built. As demand for electricity and water increases, many thermoelectric power plants will find it difficult to obtain the large quantities of water needed to maintain operations. Most of the water used in a thermoelectric power plant is used for cooling. There is a need for reducing the amount of fresh water used by power plants because thermoelectric power plants utilize significant quantities of water. For example, a 500 MW power plant that employs a once-through cooling technique uses 4.5×104 m3/h (approximately 45×106 kg/h) of water for cooling and for other process requirements.
Power plant exhaust gases release large amounts of water vapor into the atmosphere. The flue gas is a potential source for obtaining much needed cooling water for a power plant. There is almost 40% moisture (by wet coal mass basis) in lignite coal, which translates to 16% moisture by volume (wet basis) in the flue gas. For example, a 600 MW power plant firing lignite exhausts a flue gas flow rate of 2.7×106 kg/h, which includes a moisture flow rate of 0.43×106 kg/h, or about 16 wt % of the flue gas. In contrast, typical cooling tower evaporation rates for a 600 MW power plant unit are 0.7×106 kg/h.
If a power plant could recover and reuse a portion of this moisture, it could reduce its total cooling water intake requirement. The most practical way to recover water from flue gas is to use a condensing heat exchanger. The power plant could also recover latent heat due to condensation, and sensible heat due to lowering the flue gas exit temperature. Harmful acid gases such as H2SO4, HCl, and HNO3 can also be condensed by the heat exchanger to prevent these acid gases from entering the atmosphere.